BALLISTICS

Ballistics is a science that studies the movement of projectiles. A projectile may be a shell, a bullet, a rocket, an arrow or even a golf ball-anything that is hurled through the air. Ballistics is used in the design of guns, missiles and propellant explosives. It also concerns the aiming of guns and rockets. These two divisions arecalled interior ballistics and exterior ballistics. The path of a projectile is called its trajectory.

When a gun is fired, the pressure of expanding hot gases from the explosion forces the bullet or shell out of the barrel. The distance the shell travels depends mainly on the weight of the shell and the force of the explosion. This, in turn, depends on the diameter of the barrel, called its caliber.

For a shell or bullet to travel true and reach the target nose first, it must spin on its axis. Rifling inside the barrel-long spiral grooves-makes it do this. As soon as a shell leaves a gun barrel, the force of gravity starts to pull it downwards toward the ground. For maximum range, the gun barrel must be pointed upwards at an angle of 45. At steeper angles, the shell travels higher but not as far. Using laws about gravity first worked out more than 300 years ago by the great Italian scientist Galileo; we can calculate the range of a shell if we know its velocity and the firing angle. In theory, the trajectory is a curved path known as a parabola. But in practice the path is altered by air resistance, and gun sights and range tables have to take this into account. Large modern guns are aimed using radar and electronic computers.

At very high speeds, projectiles can do remarkable things. For example the force of a tornado may be sufficient to ‘fire’ a piece of straw right through a plank of wood. These situations are studied in terminal ballistics.